Endothelial Cells
The local microenvironment profoundly affects the phenotype and growth properties of vascular endothelial cells in a tissue- or organ-specific manner, but the nature of the local instructive signals is largely unknown. There is compelling evidence that the vascular endothelial growth factor (VEGF) and angiopoietin families of endothelial cell specific growth factors are essential for embryonic development and for angiogenesis in a variety of physiological and pathological circumstances [Ferrara and Alitalo, Nature Medicine, 5:1359–1364 (1999); Carmeliet, Nature Medicine, 6:389–395 (2000)]. There is also strong evidence for a local, tissue-specific, regulation of endothelial cell phenotype and growth [Aird et al., J. Cell Biol., 138:1117–1124 (1997); Stewart and Wiley, Dev. Biol., 84:183–192 (1981)]. The morphological and functional characteristics of endothelial cells vary extensively among different organs [Simionescu and Simionescu, Cell and Tissue Biology, Urban and Schwarzemberg, Baltimore, (1988) pp. 355–398]. Furthermore, the site of application determines the properties of new vessels to an even greater extent than the type of angiogenic factor tested [Dellian et al., Am. J. Pathology, 149:59–71 (1996); Roberts et al., Am. J. Pathology, 153:1239–1248 (1998)]. The molecular basis for this influence of the local microenvironment on the properties of the vasculature is unknown, but it is believed that the specialized stroma plays a major role [Dellian, supra]. Conceivably, an integrated network of stimuli, which may include tissue-specific secreted proteins, in addition to cellular and extracellular matrix components, functions to determine the structure and function as well as modulate growth of the resident endothelium.
Thus there is a current need to identify and characterize novel growth and differentiation factors that influence the growth and/or differentiation of endothelial cells. In addition to increasing our knowledge of the development of the vasculature, such compounds could be useful in the diagnosis and treatment of conditions associated with vascular tissue.
Hormone Secreting Cells
While there has been progress in the advancement of science and medical therapies, there is still a need for new treatments for the medical ailments of society. One approach to finding new treatments has been to study how the organism operates. In particular, of interest is how signaling cells control the behavior of the organism. For example, endocrine cells secrete signaling molecules called hormones wherein malfimctioning of secretion of these hormones can lead to a variety of disorders.
Cells specialized for secretion of hormones include the cells of gonads, secreting testosterone (Leydig cell of testis), estrogen (theca interna cell of ovarian follicle) and progesterone (corpus luteum cell of ruptured ovarian follicle). While there are a variety of treatments in the medical field which utilize exogenous administration of testosterone, estrogen and progesterone, there remains a need to regulate the cells which produce these hormones.
Other cells specialized for secretion of hormones include the cells of the adrenal gland and the cells of the digestive system. For example, cells of the adrenal gland secrete epinephrine, norepinephrine and steroid hormones such as mineralocorticoids and glucocorticoids. Of particular interest is cortisol which is produced in the cortex of the adrenal gland and which influences the metabolism of many cell types. Cells of the digestive system include those of the pancreas which secretes insulin. Insulin is secreted by the islets of Langerhans and is essential for the metabolism of carbohydrates. Insulin is used in the treatment and control of diabetes mellitus, however, there is still a need for efficient treatments for disorders such as diabetes. Other hormones of interest of the gut and respiratory tract include serotonin, endorphin, somatostatin, gastrin, secretin, cholecystokinin, glucagon and bombesin.
There are numerous diseases and disorders associated with hormone secreting cells, in particular steroidogenic endothelial cells within endocrine glands. It would, therefore, be desirable to identify growth factors specifically affecting such endothelial cells. Such endothelial cell specific growth factors would be valuable tools for diagnosing and treating disorders associated with such cell types, and for identifying further drug candidates useful in diagnosis and treatment of such diseases.